Block copolymers for optical data storage

ABSTRACT

The invention relates to block copolymers for optical data storage.

[0001] The invention relates to block polymers and the use of the latterfor optical data storage.

[0002] Photoaddressable polymers are known (Polymers as electroopticaland fotooptical active media, V. P. Shibaev (ed.), Springer Verlag, NewYork 1995). Particularly suitable for this purpose are side-grouppolymers, of which the group of the copolymers is distinguished by verywide possibilities in the variation of the properties. Their specialpeculiarity is that their optical properties such as absorption,emission, reflection, birefringence, scatter may be changed reversiblyby light induction. Polymers of this kind have a particular comb-likestructure: on a linear spine sit—connected by molecule parts acting asspacers—side groups which may absorb electromagnetic radiation. Examplesof this kind are dye molecules, in particular the side-group polymerscontaining azobenzene groups according to U.S. Pat. No. 5,173,381. Saidsubstances are characterised by the capacity to form a directionalbirefringence when irradiated with polarised light. The inscribedbirefringence patterns may be made visible in the polarised light.

[0003] It is furthermore known that there may be inscribed in layers ofsaid polymers at any point with polarised light a locally limitedbirefringence whose main axis moves in sympathy on the rotation of thepolarising direction (K. Anderle, R. Birenheide, M. Eich, J. H.Wendorff, Makromol. Chem., Rapid Conmun. 10 477-483 (1989), J. Stumpe etal., 20th Freiburg Working Conference on Liquid Crystals 1991).

[0004] Suitable in principle for the production of the photoaddressablesubstrate are all polymers into which a directional birefringence may beinscribed (Polymers as electrooptical and fotooptical active media, V.P. Shibaev (ed.), Springer Verlag, New York 1995; Natansohn et al.,Chem. Mater. 1993, 403-411). These are in particular side-grouppolymers, of which the copolymers are preferred. Preferred suchcopolymers are disclosed for example in DE-A 43 10 368 and DE-A 44 34966. Preferably they contain a poly(meth)acrylate main chain acting as aspine with recurring

[0005] units, wherein R represents hydrogen or methyl, the dots indicatethe linkage of the further units of the main chain and the side chain islinked to the carbonyl group.

[0006] From DE-A-19 620 588 are known polymers which contain side chainsbranching off from the main chain and having the formulae S-T-Q-P withP=A, M:

-S¹-T¹-Q¹-A  (I) and

-S²-T²-Q²-M  (II),

[0007] wherein

[0008] S¹, S² signify independently of one another the atoms O, S or thegroup NR¹,

[0009] R¹ signifies hydrogen or C₁-C₄ alkyl,

[0010] T¹, T² signify independently of one another the group (CH₂)_(n),which optionally may be interrupted by —O—, —NR¹— or —OSiR¹ ₂O— and/orsubstituted by methyl or ethyl, and

[0011] n signifies the numbers 2, 3 or 4,

[0012] Q¹, Q² a divalent group,

[0013] A a unit which may absorb electromagnetic radiation and

[0014] M a polarisable aromatic group having at least 12 π-electrons.

[0015] The function of M is cO—Operative re-orientation together withthe actual absorbing units. This results in a strengthening of there-orientation and stabilisation of the re-oriented molecules.

[0016] Particularly preferred are polymers in which

[0017] Q¹, Q² signify independently of one another Z¹, Z² or the group-Z¹-X-Z²-, wherein

[0018] Z¹, Z2 signify independently of one another the groups —S—,—SO_(2—), —O—, —COO—, —OCO—, 13 CONR¹—, —NR¹CO—, —NR¹—, —N═N—, —CH═CH—,—N═CH—, —CH═N— or the group —(CH₂)_(m—) with m=1 or 2 and

[0019] X signifies a 5- or 6-member cycloaliphatic, aromatic orheterocyclic ring, for the case Z¹=—COO— or —CONRA— a direct link or thegroup —(CH═CH)_(m—), where m has the signification given above,

[0020] A signifies the residue of a mono-azo dye which absorbs in thewavelength range between 650 and 340 nm, and

[0021] M signifies the residue of a polarised and further polarisablearomatic, linearly structured system having at least 12π-electrons.

[0022] Preferred groups A correspond to the formula

[0023] where

[0024] R¹ to R⁷ signify independently of one another hydrogen, hydroxyl,halogen, nitro, cyano, C₁-C₄-alkyl, C₁-C₄-alkoxy, CF₃, CCl₃, CBr₃,SO₂CF₃, C₁-C₆-alkyl-sulfonyl, phenylsulfonyl, C₁-C₆-alkylaminosulfonyl,phenylaminosulfonyl, aminocarbonyl, C₁-C₆-alkylaminocarbonyl,phenylaminocarbonyl or COOR¹.

[0025] Preferred groups M correspond to the formula

[0026] where

[0027] R⁸ to R¹³ signify independently of one another hydrogen,hydroxyl, halogen, nitro, cyano, C₁-C₄-alkyl, C₁-C₄-alkoxy, CF₃, CCl₃,CBr₃, SO₂CF₃, C₁-C₆-alkyl-sulfonyl, phenylsulfonyl,C₁-C₆-alkylaminosulfonyl, phenylaminosulfonyl aminocarbonyl,C₁-C₆-alkylaminocarbonyl, phenylaminocarbonyl or COOR¹ and

[0028] Y signifies —COO—, —OCO—, —CONH—, —NHCO—, —O—, —NH—, —N(CH₃)— ora single bond.

[0029] Amorphous polymers are preferred, i.e. ones which do not formmacroscopically discernible liquid crystalline phases. “Amorphous” meansan optically isotropic state. Such polymers neither scatter visiblelight nor possess a birefringence in the initial isotropic state withoutthe action of external forces.

[0030] A process for producing the radical polymerisation is likewisementioned.

[0031] Materials for holographic data storage are likewise known.

[0032] Holography is a process in which, through the interference of twocoherent beams of light (signal wave and reference wave), objects may beimaged in suitable storage materials and said images may be read outagain with light (reading beam) (D. Gabor, Nature 151, 454 (1948), N. H.Farath, Advances in holography, Vol. 3, Marcel Decker (1977), H. M.Smith, Holographic recording materials, Springer (1977). By changing theangle between signal and reference wave on the one hand and theholographic storage material on the other, numerous holograms may beinscribed into the material and finally also read out againindividually. As a rule, the light of a laser serves as a coherent lightsource. Many different materials are described as storage material, e.g.inorganic crystals such as LiNbO₃ (e.g.), organic polymers (e.g. M.Eich, J. H. Wendorff, Makromol. Chem., Rapid Commun. 8, 467 (1987), J.H. Wendorff, M. Eich, Mol. Cryst. Liq. Cryst. 169, 133 (1989)) orFotopolymere (Uh-Sock Rhee et al., Applied Optics, 34 (5), 846 (1995)).

[0033] Said materials, however, still do not meet all the requirementsof a holographic recording medium. In particular they do not possessadequate stabilities of the inscribed hologram. Multiple inscription ispossible to only a limited extent as a rule, since with the inscriptionof a new hologram the hologram already inscribed is overwritten andhence erased. This applies in particular to inorganic crystals, whichare subjected to a complex heat treatment in order to compensate forsaid stability problems. Photopolymers conversely exhibit the problem ofshrinkage, which has a negative effect on the holographic imagingproperties.

[0034] Materials with high stability of the inscribed holograms arelikewise known, e.g. from EP-A 0 704 513.

[0035] The high optical density of said materials does not howeverpermit the production of high-volume holographic stores, such as arerequired for the storage of numerous holograms in a storage material.

[0036] There was therefore a requirement for a material which issuitable for the production of sufficiently thick high-volumeholographic stores. The thickness of the materials should lie in therange of millimetres. With the materials of the prior art, thepenetration of the laser beams almost always presents problems by virtueof the high optical density.

[0037] The object was an avoidance of this problem with simultaneousguaranteeing of the high storage efficiency. It can be observed thatwith increasing dilution of the dyes in copolymers (decrease in theoptical density) a decrease in the holographic diffraction efficiency isalso to be observed.

[0038] Surprisingly it has now been found that polymers with specificarchitectures do not exhibit said disadvantage.

[0039] The present application therefore provides a polymer havingvarious blocks characterised in that it consists of

[0040] at least one block (A) having at least 3 repeat units with thegeneral formula (CI)

[0041] where

[0042] R¹⁰⁰ represents hydrogen or methyl and

[0043] R⁷⁰¹ represents hydrogen or C₁-C₈ linear or branched alkylwithout photo-isomerisable groups, preferably methyl, ethyl, propyl,n-butyl, particularly preferably methyl, and

[0044] at least one block (B) having repeat units with the generalformula (CII)

[0045] where

[0046] R⁷⁰² represents hydrogen or methyl and

[0047] R⁷⁰³ represents [—S—T-Q-P] and where P represents A and/or M,

[0048] where however a polymer (B) is always contained in which Prepresents A.

[0049] The side-chains branching off from the main chain, of the formulaS-T-Q-P with P=A (dye group), M (mesogen), are governed by the followingdefinitions:

S-T-Q-P=S¹-T¹-Q¹-A

S-T-Q-P=S²-T²-Q²-M

[0050] where

[0051] S¹, S² signify independently of one another the atoms O, S or thegroup NR¹,

[0052] R¹ signifies hydrogen or C₁-C₄ alkyl,

[0053] T¹, T² signify independently of one another the group (CH₂)n,which may optionally be interrupted by —O—, —NR¹- or —OSiR¹ ₂O— and/orsubstituted by methyl or ethyl,

[0054] n signifies the numbers 2, 3 or 4,

[0055] Q¹, Q² a divalent group,

[0056] A a unit which may absorb electromagnetic radiation and

[0057] M a polarisable aromatic group having at least 12 π-electrons.

[0058] The function of M is cO—Operative re-orientation together withthe actual absorbing units. This results in a strengthening of there-orientation and stabilisation of the re-oriented molecules.

[0059] Particularly preferred are polymers in which

[0060] Q¹, Q² signify independently of one another Z¹, Z² or the group-Z¹-X-Z²-, where

[0061] Z¹, Z² signify independently of one another the groups —S—,—SO₂—, —O—, —COO—, —OCO—, —CONR-, —NR¹CO—, —NR¹-, —N═N—, —CH═CH—,—N═CH—, —CH═N— or the group —(CH₂)m- with m=1 or 2 and

[0062] X signifies a 5- or 6-member cycloaliphatic, aromatic orheterocyclic ring, for the case Z¹=—COO— or —CONR¹- a direct bond or thegroup —(CH=CH)m, where m has the signification given above,

[0063] A signifies the residue of a mono-azo dye which absorbs in thewavelength range between 650 and 340 nm and

[0064] M the residue of a polarised and flurther polarisable aromatic,linearly structured system having at least 12 π-electrons.

[0065] Preferred A groups correspond to the formula

[0066] where

[0067] R² to R⁷ signify independently of one another hydrogen, hydroxyl,halogen, nitro, cyano, C₁-C₄ alkyl, C₁-C₄ alkoxy, CF₃, CCl₃, CBr₃,SO₂CF₃, C₁-C₆-alkyl-sulfonyl, phenylsulfonyl, C₁-C₆-alkylaminosulfonyl,phenylaminosulfonyl, aminocarbonyl, C₁-C₆-alkylaminocarbonyl,phenylaminocarbonyl or COOR¹.

[0068] Preferred M groups correspond to the formula

[0069] where

[0070] R⁸ to R¹³ signify independently of one another hydrogen,hydroxyl, halogen, nitro, cyano, C₁-C₄ alkyl, C₁-C₄ alkoxy, CF₃, CC1₃,CBr₃, SO₂CF₃, C₁-C₆ alkyl-sulfonyl, phenylsulfonyl,C₁-C₆-alkylaminosulfonyl, phenylaminosulfonyl, aminocarbonyl,C₁-C₆-alkylaminocarbonyl, phenylaminocarbonyl or COOR¹ and

[0071] Y signifies —COO—, —OCO—, —CONH—, —NHCO—, —O—, —NH—, —N(CH₃)— ora single bond.

[0072] Particularly good results are obtained if there are contained inthe block (A) at least 5, preferably at least 20, particularlypreferably at least 75 repeat units.

[0073] A plurality of repeat units should also be present in the block(B), at least 3, preferably at least 5, particularly preferably at least10 and most preferably of all at least 20 repeat units are contained.

[0074] Naturally it is also included by the present invention that morethan 1 block (A) and/or (B) is contained.

[0075] Very good results are obtained if the ratio of the sum of themonomers of block (B) to the sum of the monomers of block (A) liesbetween 1:1 and 1:10 000, preferably between 1:1 and 5000, particularlypreferably between 1:2 and 1:3000, very particularly preferably between1:5 and 1:1500 and most preferably of all between 1:10 and 1:1000.

[0076] Preferred are copolymers in which block (A) contains methylmethacrylate units.

[0077] Good results are achieved when blocks (B) having elements whichbear STQP are present. An improved embodiment consists in block (B)containing at least 2 different monomers which bear the general formula[STQP], wherein at least one of said monomers bears a dye group,preferably a photoisomerisable group. It is further particularlypreferable that said photoisomerisable group is an azo group. Mostparticularly preferably said group has the structure of the formula(CIV).

[0078] where

[0079] R¹⁰¹ and R¹⁰² represent independently of one another hydrogen ora nonionic substituent,

[0080] m and n represent independently of one another a whole numberfrom 0 to 4, preferably 0 to 2,

[0081] X¹⁰¹ represents the linkage with S¹⁰¹T¹⁰¹Q¹⁰¹, i.e. X¹⁰¹ has thesignification X¹⁰¹′, where X¹⁰¹′ is linked to the Q with the 2ndvalency,

[0082] X¹⁰²′ signifies X¹⁰²′-R¹⁰⁴,

[0083] X¹⁰¹′ and X¹⁰²′ represents a direct bond, —O—, —S—, —(N-R¹⁰⁵)—,—C(R¹⁰⁶R¹⁰⁷)—, —(C═O)—, —(CO—O)—, —(CO—NR105)—, —(SO₂)—, —(SO₂—O)—,—(SO₂—NR¹⁰⁵)—, —(C═NR¹⁸)— or —(CNR¹⁸—NR¹⁵)—,

[0084] R¹⁰⁴, R¹⁵ and R¹⁸ stand independently of one another forhydrogen, C₁- to C₂₀-alkyl, C₃- to C₁₀-cycloalayl, C₂- to C₂₀-alkenyl,C₆- to C₁₀-aryl, C₁- to C₂₀-alkyl—(C═O)—, C₃- to C₁₀-cycloalkyl—(C═O)—,C₂- to C₂₀-alkenyl—(C═O)—, C₆- to C₁₀-aryl—(C═O)—, C₁- toC₂₀-alkyl—(SO₂)—, C₃- to C₁₀-cycloalkyl—(SO₂)—, C₂- toC₂₀-alkenyl—(SO₂)— or C₆- to C₁₀-aryl—(SO₂)— or

[0085] X¹⁰²′-R¹⁰⁴ may represent hydrogen, halogen, cyano, nitro, CF₃ orCCl₃,

[0086] R¹⁰⁶ and R¹⁰⁷ represent independently of one another hydrogen,halogen, C₁ to C₂₀ alkyl, C₁- to C₂₀-alkoxy, C₃- to C₁₀-cycloalkyl, C₂-to C₂₀-alkenyl or C₆- to C₁₀-aryl,

[0087] S¹⁰¹ signifies the atoms O, S or the group NR^(109,)

[0088] R¹⁰⁹ signifies hydrogen or C₁-C₄-alkyl,

[0089] T¹⁰¹ signifies the group (CH₂)_(x), which may optionally beinterrupted by —O—, —N¹⁰⁹— or —OSiR¹⁰⁹ ₂O— and/or substituted by methylor ethyl, x signifies the numbers 2, 3 or 4,

[0090] Q¹⁰¹ signifies Z¹⁰¹, Z¹⁰² or the group -Z¹⁰¹-X¹⁰⁰-Z¹⁰², where

[0091] Z¹⁰¹ and Z¹⁰² signify independently of one another the groups—S—, —SO₂—, —COO—, —OCO—, —CONR¹⁰⁹—, —NR¹⁰⁹CO—, —NR¹⁰⁹—, —N═N—, —CH═CH—,—N═CH—, —CH═N— or the group —CH₂)_(y)— with y=1 or 2 and

[0092] X¹⁰⁰ signifies a 5- or 6-member cycloaliphatic, aromatic orheterocyclic ring, for the case Z¹⁰¹=—COO— or —CONR¹⁰⁹— a direct bond orthe group —(CH═CH)_(y)—, where y has the signification given above.

[0093] By nonionic substituents are to be understood halogen, cyano,nitro, C₁- to C₂₀-alkyl, C₁- to C₂₀-alkoxy, phenoxy, C₃- toC₁₀-cycloalkyl, C₂- to C₂₀-alkenyl or C₆- to C₁₀-aryl, C₁- toC₂₀-alkyl—(C═O)—, C₆- to C₁₀-aryl—(C═O)—, C₁- to C₂₀-alkyl—(SO₂)—,C₁-C₂₀-alkyl—(C═O)—O—, C₁- to C₂₀-alkyl—(C═O)—NH—, C₆- toC₁₀-aryl—(C═O)—NH—, C₁- to C₂₀-alkyl-O—(C═O)—, C₁- toC₂₀-alkyl-NH—(C═O)— or C₆- to C₁₀-aryl-NH—(C═O)—.

[0094] The alkyl, cycloalkyl, alkenyl and aryl groups may for their partbe substituted by up to 3 groups from the series halogen, cyano, nitro,C₁- to C₂₀-alkyl, C₁- to C₂₀-alkoxy,

[0095] C₃- to C₁₀-cycloalkyl, C₂- to C₂₀-alkenyl or C₆- to C₁₀-aryl andthe alkyl and alkenyl groups may be straight-chain or branched.

[0096] By halogen is to be understood fluorine, chlorine, bromine andiodine, in particular fluorine and chlorine.

[0097] Preferred are polymers characterised in that the monomers withthe photoisomerisable group exhibit the formula (CV)

[0098] where

[0099] R¹⁰² represents hydrogen or methyl and

[0100] the other groups possess the signification given above.

[0101] Particularly preferred monomers which bear the photoisomerisablegroup (A) are:

[0102] Likewise preferred are block copolymers characterised in thatthey contain in addition to monomers with the photoisomerisable group A,preferably those having the formula (CV), monomers with the polarisablearomatic group M having the formula (CVI)

[0103] where

[0104] Z²⁰⁰ represents a group with the formulae

[0105] where

[0106] B represents O, S or N-C₁- to C₄-alkyl,

[0107] X¹⁰³ represents -X¹⁰³′—(Q¹⁰²)_(j)-T¹⁰²-S¹⁰²—

[0108] X¹⁰⁴ represents X¹⁰⁴′-R²⁰³,

[0109] X¹⁰³ and X¹⁰⁴′ represent independently of one another a directbond, —O—, —S—, —(N—R²⁰⁵)—, —C(R²⁰⁶R²⁰⁷)—, —(C═O)—, —(CO—O)—,—(CO—NR²⁰⁵)—, —(SO₂)—, —(SO₂—O)—, —(SO₂—NR²⁰⁵)—, —(C═NR²⁰⁸)— or—(CNR²⁰⁸—NR²⁰⁵)—,

[0110] R^(205,) R²⁰⁸ and R²⁰³ represent independently of one anotherhydrogen, C₁- to C₂₀-alkyl, C₃- to C₁₀-cycloalkyl, C₂- to C₂₀-alkenyl,C₆-C₁₀-aryl, C₁-C₂₀-alkyl-(C═O)—, C₃-C₁₀-cycloalkyl-(C═O)—,C₂-C₂₀-alkenyl-(C═O)—, C₆- to C₁₀-aryl-(C═O)—, C₁- to C₂₀-alkyl-(SO₂)—,C₃- to C₁₀-cycloalkyl-(SO₂)—, C₂- to C₂₀-alkenyl-(SO₂)— or C₆- toC₁₀-aryl-(SO₂)— or

[0111] X¹⁰⁴′-R²⁰³ may represent hydrogen, halogen, cyano, nitro, CF₃ orCCl₃,

[0112] R²⁰⁶ and R²⁰⁷ represent independently of one another hydrogen,halogen, C₁ to C₂₀-alkyl, C_(1—) to C₂₀-alkoxy, C₃- to C₁₀-cycloalkyl,C₂- to C₂₀-alkenyl or C₆- to C₁₀-aryl,

[0113] Y²⁰⁰ represents a single bond, —COO—, OCO—, —CONH—, —NHCO—,—CON(CH₃)—, —N(CH₃)CO—, —O—, —NH— or —N(CH₃)—,

[0114] R²⁰¹, R²⁰², R²⁰⁶ represent independently of one another hydrogen,halogen, cyano, nitro, C₁- to C₂₀-alkyl, C₁- to C₂₀-alkoxy, phenoxy, C₃-to C₁₀-cycloalkyl, C₂- to C₂₀-alkenyl or C₆- to C₁₀-aryl, C₁- toC₂₀-alkyl-(C═O)—, C₆- to C₁₀-aryl-(C═O)—, C₁- to C₂₀-alkyl-(SO₂)—,C₁-C₂₀-alkyl-(C═O)—O—, C₁- to C₂₀-alkyl-(C═O)—NH—, C₆- toC₁₀-aryl-(C═O)—NH—, C₁- to C₂₀-alkyl-O—(C═O)—, C₁- toC₂₀-alkyl-NH—(C═O)— or C₆- to C₁₀-aryl-NH—(C═O)—,

[0115] q, r and s represent independently of one another a whole numberfrom 0 to 4, preferably 0 to 2,

[0116] Q¹⁰² represents —O—, —S—, (N—R²⁰⁵)—, a—C(R²⁰⁶R²⁰⁷)—, —(C═O)—,—(CO—O)—, —(CO—NR²⁰⁵)—, —(SO₂)—, —(SO₂-0)—, —(SO₂-NR²⁰⁵)—, —(C═NR²⁰⁸)—,—(CNR²⁰⁸—NR)——(CH₂)_(p)—, p- or m-C₆H₄— or a divalent group with theformulae

[0117]

[0118] j represents a whole number from 0 to 4, where for j>1 theindividual Q¹⁰² may have different significations,

[0119] T¹⁰² represents —(CH₂)_(p)—, where the chain may be interruptedby —O—, —NR²⁰⁹— or —OSiR²²⁰—,

[0120] S¹⁰² represents a direct bond, —O—, —S— or NR²⁰⁹—,

[0121] p represents a whole number from 2 to 12, preferably 2 to 8, inparticular 2 to 4,

[0122] R²⁰⁹ represents hydrogen, methyl, ethyl or propyl and

[0123] R²²⁰ represents methyl or ethyl. Preferred monomers having suchgroups exhibiting form anisotropy M then have the formula (CVII):

[0124]

[0125] where

[0126] R¹⁰² represents hydrogen or methyl and

[0127] the other groups have the meanings given above.

[0128] Particularly preferred monomers exhibiting form anisotropy withthe formula (CVII) are for example:

[0129] The block copolymers according to the invention contain inaddition to at least one polymer (A)

[0130] a) preferably at least one polymer (B) which consists of monomerswith the formula (CV),

[0131] b) preferably at least one polymer (B) which consists of monomerswith the formula (CV) and at least one polymer (B) which consists ofmonomers with the formula (CVII),

[0132] c) particularly preferably at least one polymer which consists ofmonomers with the formula (CV) and monomers with the formula (CVII).

[0133] In case a) the monomers with the formula (CV) of polymer (B) maybe identical or different. The same applies to the monomers (CV) and/or(CVII) in polymers (B) in the cases b) and c). The monomers with theformula (CV) and the formula (CVII) are used in the block copolymersaccording to the invention in the ratio 1:1 to 1:30, preferably 1:1 to1:20, particularly preferably 1:2 to 1:10.

[0134] In addition to the controlled radical polymerisation, it is alsopossible to produce the AB block copolymers described in the patent by acombination of anionic polymerisation and subsequent polymer-analogousreaction. In this case first of all an AB block copolymer is produced bysequential, living anionic polymerisation, which contains in a block,either A or B, a protected functional group. After the polymerisationthe functional group is liberated. A photoisomerisable and/or mesogenicside group is introduced by polymer-analogous conversion. The sidegroups are identical with the structure given in formula (IV). Thepolymer-analogous conversion is preferably to take place with aconversion rate of 20 to 100%.

[0135] An important parameter for the present invention is the opticaldensity, which possesses for the wavelength of the writing laser and asample thickness of 1 mm, a value ≦2, preferably ≦1, particularlypreferably of ≦0.3. In this way it may be ensured that the actinic lightleads to a homogeneous transillumination of the entire storage mediumand a thick hologram may be produced. The optical density may bedetermined with commercial UV/VIS spectrometers (e.g. CARY, 4G).

[0136] In particular the block copolymer according to the invention is amaterial which has a transilluminated thickness of ≧0.1 mm, particularly0.5 mm, preferably ≧1 mm and most particularly preferably not greaterthan 1 cm.

[0137] The grouping which interacts with the electromagnetic radiationis preferably a dye described above, which absorbs preferably in thewavelength range between 390 and 800 nm, particularly preferably aroundthe range 400 to 650 nm and most particularly preferably in the rangefrom 510 to 570 um. An Nd:YAG laser (λ=532 um) may be used as a typicaltest laser

[0138] For the reading the recording material is no longer exposed totwo interfering beams, as during the writing, but only to one beam, thereading beam.

[0139] The wavelength of the reading beam is preferably longer than thatof the signal and reference waves, for example 70 to 500 nm longer.Reading with the wavelength of the writing laser is however alsopossible and is employed in particular during the commercial use oflarge-volume holographic stores. In this case, however, during thereading operation the energy of the reading beam is lowered either bythe reduction of the exposure intensity or the exposure time or by areduction of the exposure intensity and the exposure time.

[0140] The optical density of the block copolymer according to theinvention is determined by the concentration of the at least one dye inthe copolymeric material.

[0141] Method for the synthesis of functionalised AB block copolymersaccording to the invention by controlled polymerisation

[0142] The synthesis of AB block copolymers with functionalisedmethacrylates and acrylates is produced with the aid of a controlledradical polymerisation or a combination of anionic polymerisation andsubsequent polymer-analogous reaction.

[0143] In this case a non-functionalised block forms the matrix (Ablock), while in the B block the photo-active or mesogenic side chainsare bonded to the acrylate or methacrylate monomers via spacers with alength of 0-6 CH₂ units. The B block may further consist of a staticcopolymer of photo-active or mesogenic monomers, wherein the proportionof the photo-active component may lie between 0 and 100%. In comparisonwith the prior art (e.g. Kathryn L. Beers, Sohyun Boo, Scott G. Gaynor,and Krzysztof Matyjaszewski, Macromolecules 1999, 32, 5772-5776; AndreasMihlbach, Scott G. Gaynor, Krzysztof Matyaszewski, Macromolecules 1999,31, 6046-6052; Devon A. Shipp, Jen-Lung Wang and KrzysztofMatyjaszewski, Macromolecules 1999, 32, 5772-5776) in the controlledradical polymerisation the polymers described here are distinguished bythe fact that use is made for the first time in a controlled radicalpolymerisation of monomers which bear as side chains a group A which mayabsorb electromagnetic radiation in the visible light wavelength region,and/or bear a group M which represents a mesogenic group exhibiting formanisotropy.

[0144] In the first step a homopolymer is prepared which is used asmacroinitiator for the second component of the block copolymer (BCP).Preferably the macroinitiator is a non-functionalised homopolymer whichserves as a solubility promoter in the polymerisation of thefunctionalised monomers.

[0145] A further possibility for the synthesis of the desired blockpolymers consists in the use of the technique of anionic polymerisationwith subsequent polymer-analogous conversion for the introduction of theside group.

[0146] Use is made as the monomers to be functionalised later ofmethacrylic acid derivatives which bear instead of the OH group anOH—(CH₂)_(n)—OH group, where 2 to 6 is possible as n. For the anionicpolymerisation the OH group is masked by a protective group, whereintrimethylsilyl or tert.butyldimethylsilyl are described as particularlyfavourable.

EXAMPLES Example I Synthesis of Compound BCP1

[0147]

[0148] The polymerisation is carried out according to the followingsynthesis specification, the macroinitiator being prepared first of all.

[0149] The addition of the monomer (n-butyl acrylate), the ligand(PMDETA), decane as inner standard and the liquid initiator (P) takesplace under inert gas atmosphere. 2 g of n-butyl acrylate, 5 g of ethylacetate and 44.8 mg of copper(I)bromide are used for the polymerisationin each case. 0.2 g of decane are used as internal standard for theconversion determination by gas chromatography.

[0150] The polymerisation is concluded by rapid cooling to 5° C. andaddition of THF. The separation of the copper bromide out of the polymersolution takes place by filtration on activated aluminium oxide. Bothacid and basic material may be used for this. The polymerisationtemperature amounted to 80° C. The preparation of the block copolymertakes place by dissolving of the corresponding amount of themacroinitiator described above (n-polybutyl acrylate, M_(n)=13000 g/mol)in ethyl acetate (1 ml). The monomer (570 mg) (see I) is likewisedissolved in ethyl acetate (2.5 ml) and both solutions are degassed. Theaddition of the ligand (48.5 μl) (PMDETA) and copper(I)bromide (33 mg)takes place in the inert atmosphere.

Example II Synthesis of Compound BCP2

[0151]

[0152] The macroinitiator is prepared analogously to Example 1, but ablock length of 19000 g/mol referred to styrene calibration is preparedby corresponding reduced addition of the amount of initiator.

[0153] The initiator prepared is used analogously to the abovespecification for the preparation of the block copolymer. In this case1.5 g of the macroinitiator (n-polybutyl acrylate, M_(n)=19000 g/mol)are dissolved in 1.5 ml of ethyl acetate. The functionalised monomersgiven below (II: 151 mg, III: 499 mg) are dissolved in 2 ml of ethylacetate and both solutions are mixed after the degassing under inertatmosphere.

[0154] 23.8 mg of copper(I)bromide and 34.8 μl of the ligand (PMDETA)are added to the solution. The reaction is carried out at 55° C. Theworking up of the polymer takes place analogously to Example 1.

[0155] The B block consists here, however, of a statistical copolymerwhose monomers bear side groups which correspond to the properties ofthe above-mentioned A or M type. The molar ratios amount to 30:70 (A:M)here.

[0156] Alternatively an anionic polymerisation and polymer-analogousconversion may take place.

Example III Synthesis of the Following Compound

[0157]

[0158] The polymerisation is carried out according to the followingsynthesis specification. 400 ml of THF are heated for several days overpotassium and then fed into a reactor (inert gas) under inert gasatmosphere. The solution is cooled to 55° C. The 1.69 ml initiatorsolution (1.3 molar sec. BuLi solution in hexane) and then 0.85 ml ofdiphenyl ethylene solution are added through a septum. After 5 minutesthe hydroxyethyl methacrylate (10.4 g) protected bytert.butyldimethylsilyl is added via the septum. After 40 minutes themethyl methacrylate (105 g) is added to the reactor via an ampoule andthe temperature is set at 0° C. After 30 minutes the polymerisation isconcluded by the addition of 1 ml of methanol. The polymer isprecipitated in a 10-fold excess of methanol solution andre-precipitated several times prior to further use.

[0159] The silyl protection group is split off from the block copolymerby the block copolymer being dissolved in dioxane and a 4-fold excess ofsemi-concentrated hydrochloric acid is added. The unprotected blockcopolymer is dried for several days under high vacuum prior to thepolymer-analogous reaction. The polymer is then dissolved in dry THF andthe azo acid chloride is added slowly drop-wise dissolved in N-methylpyrrolidone under inert gas atmosphere. To accelerate the reaction, anexcess of pyridine is added. The reaction time amounts to 48 h at 55° C.After the reaction the unreacted azo dye is separated.

[0160] The alternative synthesis of AB block copolymers takes place byanionic polymerisation of methacrylates and protected methacrylates.

[0161] The polymerisation takes place according to general specification(Henry L. Hsieh, Roderic P. Quirk, 1996, Marcel Dekker, in particular p.640 ff.) on the anionic polymerisation of methacrylates in THF. Thesplitting off of the protective group takes place by precipitation ofthe polymer in methanol or dissolving in dioxane and heating with theaddition of dilute hydrochloric acid. The bonding of the side group,which may bear a group A, which may absorb electromagnetic radiation,and/or a group M, which represents a mesogenic group exhibiting formanisotropy, takes place by conversion with an acid chloride whichrepresents the terminal group of the side chain.

[0162] In the application optical elements are understood to be thediffractive and holographic optical elements.

[0163] The application therefore provides a method for preparing the ADblock copolymers according to the invention, wherein polymers withdefined structure and molecular weight of the individual blocks in thecopolymer are synthesised by controlled polymerisation and there areused as techniques here both the anionic polymerisation of monomers,including in some cases protected OH-functionalised monomers on anacrylate and methacrylate base, and controlled radical polymerisation offunctionalised monomers.

[0164] The copolymers according to the invention may be used excellentlyfor the production of optical elements and stores, which are usedpreferably for the storage of data, wherein particularly preferablyholography is used.

[0165] This is justified by the fact that very good information may beinscribed into the optical element by means of a laser beam.

[0166] The application preferably provides high-volume stores containingat least one copolymer according to the invention, which possess atransilluminated thickness of ≧0.1 mm, preferably ≧0.5 mm, particularlypreferably ≧1.0 mm, most particularly preferably between 1 mm and 1 cm.

[0167] The production of high-volume stores in the form of films,sheets, plates and cuboids is possible without cumbersome orientationmethods with the use of external fields and/or surface effects beingrequired. They may be applied to substrates by means of spin coating,dipping, pouring or other coating methods easy to mastertechnologically, brought between two transparent plates by pressing orinflow, or simply prepared as a self-supporting material by pouring orextruding. Such films, sheets, plates and cuboids may be produced byabrupt cooling, i.e. by means of a cooling rate of >100 K/min, or byrapid extraction of the solvent also out of liquid-crystalline polymersor oligomers which contain structural elements in the sense described.

[0168] The layer thickness is ≧0.1 mm, preferably ≧0.5 mm, particularlypreferably ≧1 mm. A particularly preferred preparation method for layersin the millimetre range is represented by the injection moulding method.In this the polymer melt is pressed through a nozzle into a formingsupport, from which it may be removed after the cooling. The applicationalso provides high-volume stores which are protected against mechanicaldamage by a protective layer.

[0169] The method of holographic data storage is described for examplein LASER FOCUS WORLD, NOVEMBER 1996, p. 81 ff.

[0170] During the writing of a hologram the polymer films describedabove are irradiated by two coherent laser beams of a wavelength whichproduces the required light-induced reorientations. The one beam, theobject beam, contains the optical information to be stored, for examplethe intensity curve which results from the passage of a light beamthrough a two-dimensional, chessboard-type pixel structure (data side).In principle, however, there may be used as the object beam, light whichis diffracted, scattered or reflected from any two- or three-dimensionalobject. On the storage medium the object beam is caused to undergointerference with the second laser beam, the reference beam, which is ingeneral a level or circular wave. The resulting interference pattern isimpressed in the storage medium as a modulation of the optical constants(refractive index and/or absorption coefficient). Said modulationtraverses the whole of the irradiated area, in particular the thicknessof the storage medium. If now the object beam is blocked off and themedium is illuminated solely with the reference beam, the modulatedstorage medium functions as a kind of diffraction grating for thereference beam. The intensity distribution resulting from thediffraction corresponds to the intensity distribution which issued fromthe object to be stored, so that it may no longer be distinguishedwhether the light comes from the object itself, or whether it results byvirtue of the diffraction of the reference beam.

[0171] Various multiplex methods may be used for the storage of variousholograms at a sample position: wavelength multiplexing, shiftmultiplexing, phase multiplexing, peristrophic multiplexing and/orangular multiplexing. With angular multiplexing the angle between thestorage medium, in which a hologram has been stored under the currentangles, and the reference beam is changed. From a certain change inangle onwards the original hologram disappears (Bragg mismatch): theincident reference beam may no longer be deflected by the storage mediumfor the reconstruction of the object. The angle from which this occursdepends critically on the thickness of the storage medium (and on themodulation of the optical constants which is produced in the medium):the thicker the medium, the smaller is the angle through which thereference beam must be changed.

[0172] In said new angular configuration a further hologram may beinscribed. The reading out of said hologram functions again in preciselythe same angular configuration between storage medium and reference beamas it was written in.

[0173] Several holograms may therefore be inscribed at the same point ofthe storage medium by successive changing of the angle between mediumand writing beams.

[0174] The application provides all the polymers, methods and usesdescribed in the claims. The application provides a method for producingoptical elements and storage elements, preferably holographichigh-volume stores, by injection moulding.

[0175] The application provides a method for producing optical elementsand storage elements, preferably holographic high-volume stores, byinjection moulding, wherein in addition the moulding is polished.

[0176] A polishing of the mouldings takes place until such time as thewave-front distortion and the surface phenority is better than$\frac{\lambda}{10}.$

[0177] The wave-front distortion is determined by the imaging of themoulding onto e.g. a CCD camera during the exposure of the latter to abeam of the writing laser of the wavelength λ.

[0178] The application provides a method for producing optical elementsand storage elements, preferably holographic high-volume stores, byinjection moulding, wherein in addition a transparent protective layeris applied.

[0179] The application provides optical elements and stores, preferablyhigh-volume stores, particularly preferably holographic high-volumestores, according to the invention.

1. A polymer having various blocks, characterised in that it consists ofat least one block (A) having at least 3 repeat units with the generalformula (CI)

where R¹⁰⁰ represents hydrogen or methyl and R⁷⁰¹ represents hydrogen orC₁-C₈ linear or branched alkyl without photoisomerisable groups,preferably methyl, ethyl, propyl, n-butyl, particularly preferablymethyl, and at least one block (b) having repeat units with the generalformula (cII)

where R⁷⁰² represents hydrogen or methyl and R⁷⁰³ represents [S-T-Q-P]and where P represents A and/or M, where however one or more blocks ofpolymer (B) are always contained in which P represents A, whereside-chains branching off from the main chain, of the formula S-T-Q-Pwith P=A (dye group), M (mesogen), are generally governed by thefollowing definitions: S-T-Q-P=S¹-T¹-Q¹-A S-T-Q-P=S²-T²-Q²-M where S¹,S² signify independently of one another the atoms O, S or the group NR¹,R¹ signifies hydrogen or C₁-C₄ alkyl, T¹, T² signify independently ofone another the group (CH₂)_(n), which may optionally be interrupted by—O—, —NR¹— or —OSiR¹ ₂O— and/or substituted by methyl or ethyl, nsignifies the numbers 2, 3 or 4, Q¹, Q² a divalent group, A a unit whichmay absorb electromagnetic radiation and M a polarisable aromatic grouphaving at least 12 π-electrons.
 2. A block polymer according to claim 1,characterised in that at least five repeat units are contained in theblock (A).
 3. A block polymer according to claim 1 and/or 2,characterised in that at least three repeat units are contained in theblock (B).
 4. A block polymer according to one or more of claims 1 to 3,characterised in that more than 1 block (A) and/or (B) is contained. 5.A block polymer according to one or more of claims 1 to 4, characterisedin that the ratio of the sum of the monomers of block (B) to the sum ofthe monomers of block (A) lies between 1:1 and 1:10
 000. 6. A blockpolymer according to one or more of claims 1 to 5, characterised in thatblock (A) contains methyl methacrylate units.
 7. A block polymeraccording to one or more of claims 1 to 6, characterised in that block(B) contains at least two different monomers with the general formula[STQP], wherein at least one of said monomers is a photoisomerisablegroup.
 8. A block polymer according to one or more of claims 1 to 7,characterised in that block (B) contains a monomer in which thephotoisomerisable group is an azo group.
 9. A block polymer according toone or more of the preceding claims, characterised in that thephotoisomerisable group has the structure (CIV)

where R¹⁰¹ and R¹⁰² represent independently of one another hydrogen or anonionic substituent, m and n represent independently of one another awhole number from 0 to 4, preferably 0 to 2, X¹⁰¹ represents the linkagewith S¹⁰¹T¹⁰¹Q¹⁰¹, i.e. X¹⁰¹ has the signification X¹⁰¹′, where X¹⁰¹′ islinked to the Q with the 2nd valency, X¹⁰² signifies X¹⁰²′-R¹⁰⁴, X¹⁰¹′and X¹⁰²′ represent a direct bond, —O—, —S—, —(N—R¹⁰⁵)—, —C(R¹⁰⁶R¹⁰⁷)—,—(C═O)—, —(CO—O)—, —(CO-NR¹⁰⁵)—, —(SO₂)—, —(SO₂—O)—, —(SO₂—NR¹⁰⁵)—,—(C═NR¹⁸)— or —(CNR¹⁸—NR¹⁵), R¹⁰⁴, R¹⁵ and R¹⁸ represent independentlyof one another hydrogen, C₁- to C₂₀-alkyl, C₃- to C₁₀-cycloalkyl, C₂- toC₂₀-alkenyl, C₆- to C₁₀-aryl, C₁ to -C₂₀-alkyl-(C═O)—, C₃ to-C₁₀-cycloalkyl-(C═O)—, C₂ to-C₂₀-alkenyl-(C═O)—, C₆- toC₁₀-aryl-(C═O)—, C₁- to C₂₀-alkyl-(SO₂)—, C₃- to C₁₀-cycloalkyl-(SO₂)—,C₂- to C₂₀-alkenyl-(SO₂)— or C₆- to C₁₀-aryl-(SO₂)— or X¹⁰²′-R¹⁰⁴ mayrepresent hydrogen, halogen, cyano, nitro, CF₃ or CCl₃, R¹⁰⁶ and R¹⁰⁷represent independently of one another hydrogen, halogen, C₁ to C₂₀alkyl, C₁ to C₂₀-alkoxy, C₃- to C₁₀-cycloalkyl, C₂- to C₂₀-alkenyl orC₆- to C₁₀-aryl, S¹⁰¹ signifies the atoms O, S or the group NR¹⁰⁹, R¹⁰⁹signifies hydrogen or C₁-C₄-alkyl, T¹⁰¹ signifies the group (CH₂)_(x),which may optionally be interrupted by —O—, —NR¹⁰⁹— or —OSiR¹⁰⁹ ₂O—and/or substituted by methyl or ethyl, x signifies the numbers 2, 3 or4, Q¹⁰¹ signifies Z¹⁰¹, Z¹⁰² or the group -Z¹⁰¹-X¹⁰⁰-Z¹⁰²-, where Z¹⁰¹and Z¹⁰² signify independently of one another the groups —S—, —SO₂—, —O——COO—, —OCO—, —CONR¹⁰⁹—, —NR¹⁰⁹CO—, —NR¹⁰⁹—, —N═N—, —CH═CH—, —N═CH—,—CH═N— or the group —(CH₂)_(y)— with y=1 or 2 and X¹⁰⁰ signifies a 5- or6-member cycloaliphatic, aromatic or heterocyclic ring, for the caseZ¹⁰¹=—COO— or —CONR¹⁰⁹— a direct bond or the group —(CH═CH)_(y)—, wherey has the signification given above.
 10. A block polymer according toone or more of claims 1 to 9, characterised in that the monomers whichbear a photoisomerisable group exhibit the formula (CV)

where R¹⁰² represents hydrogen or methyl and the other groups have thesignification given above.
 11. A block polymer according to claim 10,wherein monomers which bear photoisomerisable groups are selected fromthe structures


12. A block polymer according to one or more of claims 1 to 11,characterised in that the polarisable aromatic groups M correspond tothe formula (CVI)

where Z²⁰⁰ represents a group with the formulae

where B represents O, S or N-C₁- to C₄-alkyl, X¹⁰³ represents-X¹⁰³′-(Q¹⁰²)_(j)-T ¹⁰²S¹⁰²-, X¹⁰⁴ represents X¹⁰⁴′-R²⁰³, X¹⁰³′ andX¹⁰⁴′ represent independently of one another a direct bond, —O—, —S—,—(N—R²⁰⁵)—, —C(R²⁰⁶R²⁰⁷)—, —(C═O)—, —(CO—O)—, —(CO—NR²⁰⁵)—, —(SO₂)—,—(SO₂—O—)—, —(SO₂—NR²⁰⁵), —(C═NR²⁰⁸)— or —(CNR²⁰⁸NR²⁰⁵) R²⁰⁵, R²⁰⁸ andR²⁰³ represent independently of one another hydrogen, C₁- to C₂₀-alkyl,C₃- to C₁₀-cycloalkyl, C₂- to C₂₀-alkenyl, C₆- to C₁₀-aryl, C₁- toC₂₀-alkyl-(C═O)—, C₃- to C₁₀-cycloalkyl-(C═O)—, C₂- toC₂₀-alkenyl-(C═O)—, C₆- to C₁₀-aryl-(C═O)—, C₁- to C₂₀-alkyl-(SO₂)—, C₃-to C₁₀-cycloalkyl-(SO₂)—, C₂- to C₂₀-alkenyl-(SO₂)— or C₆- toC₁₀-aryl-(SO₂)— or X¹⁰⁴′-R²⁰³ may represent hydrogen, halogen, cyano,nitro, CF₃ or CCl₃, R²⁰⁶ and R²⁰⁷ represent independently of one anotherhydrogen, halogen, C, to C₂₀-alkyl, C₁- to C₂₀-alkoxy, C₃- toC₁₀-cycloalkyl, C₂- to C₂₀-alkenyl or C₆- to C₁₀-aryl, Y²⁰⁰ represents asingle bond, —COO—, OCO—, —CONH—, —NHCO—, —CON(CH₃)—, —N(CH₃)CO—, —O—,—NH— or —N(CH₃)—, R²⁰¹, R²⁰², R²⁰⁶ represent independently of oneanother hydrogen, halogen, cyano, nitro, C₁- to C₂₀-alkyl, C₁- toC₂₀-alkoxy, phenoxy, C₃- to C₁₀-cycloalkyl, C₂- to C₂₀-alkenyl or C₆- toC₁₀-aryl, C₁- to C₂₀-alkyl-(C═O)—, C₆- to C₁₀-aryl-(C═O)—, C₁- toC₂₀-alkyl-(SO₂)—, C₁- to C₂₀-alkyl-(C═O)—O—, C₁- to C₂₀-alkyl-(C═O)—NH—,C₆- to C₁₀-aryl-(C═O)—NH—, C₁- to C₂₀-alkyl-O—(C═O)—, C₁- toC₂₀-alkyl-NH—(C═O)— or C₆- to C₁₀-aryl-NH—(C═O)—, q, r and s representindependently of one another a whole number from 0 to 4, preferably 0 to2, Q¹⁰² represents a —O—, —S—, —(N—R²⁰⁵)—, —C(R²⁰⁶R²⁰⁷), —(C═O),—(CO—O—), —(CO—NR²⁰⁵)—, —(SO₂)—, —(SO₂—O)—, —(SO₂—NR²⁰⁵)—, —(C═NR²⁰⁸)—,—(CNR²⁰⁸—NR²⁰⁵)—, —(CH₂)_(p)—, p- or m-C₆H₄— or a divalent group withthe formulae

j represents a whole number from 0 to 4, where for j>1 the individualQ¹⁰² may have different significations, T¹⁰² represents —(CH₂)_(p)—,where the chain may be interrupted by —O—, —NR²⁰⁹— or —OSiR²²⁰ ₂O—, S¹⁰²represents a direct bond, —O—, —S— or —NR²⁰⁹—, p represents a wholenumber from 2 to 12, preferably 2 to 8, in particular 2 to 4, R²⁰⁹represents hydrogen, methyl, ethyl or propyl and R²²⁰ represents methylor ethyl.
 13. A block polymer according to one or more of claims 1 to12, characterised in that the monomers which have a grouping exhibitingform anisotropy M possess the formula (CVII)

where R¹⁰² represents hydrogen or methyl and the other groups possessthe meanings given above.
 14. A block polymer according to claim 13,wherein monomers which bear groups exhibiting form anisotropy (M) areselected from the structures


15. A block polymer according to one or more of claims 1 to 15,characterised in that the monomers of formula (CV) and of formula (CVa)are used in the ratio 1:1 to 1:30.
 16. A block polymer according to oneor more of claims 1 to 16 , characterised in that it has an opticaldensity≦2.
 17. A method for producing the block polymers according toone or more of claims 1 to 17, wherein polymers with defined structureand molecular weight of the individual blocks in the copolymer aresynthesised by controlled polymerisation and there are used astechniques here both the anionic polymerisation of monomers, includingin some cases protected OH— functionalised monomers on an acrylate andmethacrylate base, and controlled radical polymerisation offunctionalised monomers.
 18. Use of the block polymers according to oneor more of claims 1 to 17 for producing optical elements and storageelements, preferably high-volume stores.
 19. Use according to claim 19,characterised in that the optical element is used for the storage ofdata.
 20. Use according to one or more of claims 19 to 20, characterisedin that the optical element or storage element, preferably high-volumestore, is used for the storage of data by holography.
 21. Use accordingto one or more of claims 19 to 21, characterised in that information isinscribed into the optical element and/or store by means of a laserbeam.
 22. Store, preferably high-volume store, containing at least oneblock polymer according to one or more of claims 1 to 17, wherein thelatter has a transilluminated thickness of ≧0.1 mm.
 23. Method forproducing optical elements and storage elements, preferably high-volumestores, by injection moulding according to one or more of the precedingclaims.
 24. Method according to claim 23, wherein in addition themoulding is polished.
 25. Method according to claim 23 and/or 24,wherein in addition a transparent protective layer is applied. 26.Optical elements and stores according to one or more of claims 22 to 25.